1. Field of the Invention
The present invention relates to tablets which are time-controlled controlled to release active agent at different rates in different regions of the digestive tract in order to maintain a substantially constant concentration in the blood.
2. Description of the Related Art
The development of novel peroral drug delivery systems for achieving controlled administration of the active agent with minimum dependability on drug and environmental properties, has attracted a great deal of interest. Among the first systems designed and marketed successfully was the elementary osmotic pump. This system consists of a compacted core coated with a microporous, semipermeable membrane having a delivery orifice drilled in the coating by LASER. The core tablet consists of either an osmotically active therapeutic compound or a mixture of an osmotically active agent and the therapeutic compound. The osmotic pump imbibes water, dissolving the drug in the core and the drug solution is delivered through the delivery orifice at steady state and at a rate controlled by the rate of influx of the water across the semipermeable membrane.
The delivery devices described above operate successfully for their intended use and they can deliver many beneficial agents for their intended effects. Now, it has been observed their use can be limited because they lack the necessary elements to deliver beneficial agents at the appropriate amounts for the environments encountered in the gastrointestinal tract.
It will be appreciated by those versed in the dispensing arts that if a delivery system is provided for administering at a controlled rate throughout the entire gastrointestinal tract, the different absorptive rates of the various sections of the tract will result in a change in the blood levels of the delivered compound.
The goal of the present invention is to design a system or device which contains, instead of an osmotically active agent, a dry swelling material and instead of a semipermeable membrane by spray-or dip-coating, a semipermeable shell by press-coating and an exit means through which the drug solution is expelled at a predetermined rate over a period of 8 or 14 hours for a 12 or 24 hours duration of effect. The exit means may be a delivery orifice which can be made by a stylus in the upper punch of the compression tools. The advantage of the present system is the adaptability to manufacturing on a compression coating machine, in one single step.
Once the delivery system of the present invention reaches the large intestine, where absorption of drug is slower because of mucosal viscosity of the intestinal contents, the shell of the device self-destructs destructs thus releasing the drug at an accelerated rate.
It is accordingly an object of the present invention to provide a delivery device for the oral administration of a pharmaceutically acceptable active agent to a warm-blooded animal, with increasing delivery rate, particularly to the lower portion of the small intestine and/or the colon, more particularly to the colon.
It is another object of this invention to provide a dosage form for delivering substantially all of a therapeutic drug to the colon.
It is yet another object of this invention to provide a dosage form which comprises a core tablet coated with a delay jacket for delaying the delivery of the drug to insure the time required for the dosage form to travel through the small intestine.
These, and other objects apparent to those skilled in the art from the following detailed description, are accomplished by the present invention which pertains to the delivery of a therapeutic drug to a pre-selected region of the gastrointestinal tract, by means of a drug delivery device. This drug delivery device comprises: